Many current storage subsystems have a caching controller backed up by many separate disk drives. Write requests arriving at a storage subsystem are generally cached and completion status is returned immediately. Read requests are serviced first from the storage subsystem cache and only in the event of a cache miss does the request filter down to one or more of the disk drives being managed. Performance of the storage subsystem depends on the completion of read data requests and acceptance of write data requests in the shortest time possible. Modifying the queuing behavior of the disk drives contained in such a storage subsystem can improve its performance.
Most disk drive queue sorting algorithms attempt to maximize throughput by sorting all commands in their queue for the shortest seek times with the least latency using what is called a “Shortest Access Time First” (SATF) algorithm. As recognized by the present invention, however, write requests submitted to the disk drives are intrinsically different from read requests in that acceptance of write requests have already been satisfied using the storage subsystem cache and most write commands to the disk drives are actually maintenance requests generated internally by the storage subsystem to free up cache resource. Read requests, on the other hand, are time critical in that they are storage subsystem cache misses and system performance depends on satisfying these requests in the shortest time possible.
Nevertheless, while write requests are not as important to storage subsystem performance as read requests, good throughput for write requests is still desirable to maintain the storage subsystem's ability to accept new write requests. Having made the above critical observation, the solution herein is provided.